It is known in the art relating to compression ignition or diesel engines, especially of the prechamber type, to provide an igniter or glow plug mounted in the wall of and extending into the combustion chamber to provide a heat source to aid ignition of the charge during starting. Generally such glow plugs are electrically heated and are required to operate only during starting and warm-up of the engine. Thereafter, temperatures in the combustion chamber reach a point where reliable compression ignition is obtained without the need for added heat.
However, test results have indicated that the presence of a glow plug unit in the combustion chamber or prechamber of the diesel engine during normal running may have an adverse effect upon exhaust emissions and operating efficiency. In particular, it appears the glow plug may represent an obstruction to gas flow which may increase the production of particulates during combustion. The obstructing effect of the glow plug may be reduced by streamlining or retracting the plug unit to reduce or eliminate its interference with swirl or other normal gas flow patterns within a prechamber.
It has been proposed to retract a glow plug igniter into the combustion chamber wall when not in operation to remove it from interfering with swirl and air flow in the combustion or precombustion chamber during engine operation after the warm-up period. Glow plug retraction arrangements are shown, for example, in U.S. Pat. Nos. 1,280,748 Jernberg, 1,441,711 Petter and 4,240,392 Matayoshi et al. The latter disclosure shows straightforward direct acting electrical solenoid and hydraulic actuating devices for inserting and maintaining glow plug units in a combustion chamber during operation. However, such arrangements may not be the most effective and may require more power to operate than is desirable.